This research with hamsters and rats will further integrate the fields of behavioral endocrinology and biological rhythms. Experiments designed for circadian and ultradian rhythm analysis will benefit from the established methods practiced by researchers studying hormones and behavior or biological rhythms. Forthcoming projects include studies which examine 1) modification of ultradian eating rhythm periodicity by light cycles which are known to lengthen or shorten circadian periodicity; 2) neural substrates mediating circadian rhythm regulation and the relationship with ultradian rhythms; and 3) hormonal modification of behavioral and physiological rhythm frequency.